Checking back in to report that I picked up a legacy Twin for a ridiculously low price and it works beautifully. Eliminated two 10' runs of RG6 & a SW21 on one receiver and was able to merge in the output from my 61.5 dish into my other SW21 without changing any of my cabling except out at my dish "array."
I had some fun running around my yard, testing out potential 61.5 dish locations. I hooked up a spare 4700 receiver to a 13" B&W TV and put both on a rolling handcart with a 100' extension cord. I horizontally "mounted" my Dish 300 w/arm on a 3' long 2"x4" and carried it and a plastic bucket around while pulling the cart. When arriving to a potential spot, I put the bucket on the ground, open side down. Laid the 2x4 across it, lining up the Dish 300 with my compass. Then slowly adjusting it while reading the signal meter on the TV. Got to where I could line up 61.5 in 1-2 minutes from any spot. In fact, I found it twice holding the Dish 300 by hand.
After all of that, I ended up putting it right next to my Dish 500 pole. I didn't expect to see 61.5 from there as my neighbor's oak tree was directly in line with the bird. But it must have been just over the tree. When I moved 10' closer to the tree, I couldn't find it anymore. I mounted the 300 a foot higher than the 500, but I suppose the oak tree might block it in a couple of years. Not going to worry about that for now because putting it at the same spot sure simplied the installation.
As I have another 300 in the garage, and another LNB, I am now tempted to rig it up to take on vacations with me. It is so easy to align.